The invention relates to an image display device comprising a light modulation panel, a light conductor arranged opposite the light modulation panel, and a light source coupled to the light conductor.
The invention also relates to a method of manufacturing a light conductor for such an image display device.
The light conductor may be an optical element or may have an air gap.
In such an image display device, which is known from U.S. Pat. No. 5,896,232, the light conductor comprises a plurality of parallel extending elements reflecting light having a first direction of polarization and being transparent to light having a second direction of polarization. The image display device is used, inter alia, in head-mounted display devices (HMD) and projection televisions. LCDs which are either transparent or reflective are regularly used as light modulation panels. In a reflective LCD, the LCD is illuminated from the same side as the side from which it is viewed. Notably for HMDs, the light source and the associated light conductor should be as thin as possible so that the HMD can be given a relatively compact form. This has the advantage that a lens situated on a side of the light conductor remote from the light modulation panel is situated relatively close to the light conductor, which is favorable for achieving an optimal magnification.
In the image display device described in the above-mentioned United States patent, the light source is situated on a side of the light conductor remote from the light modulation panel. Consequently, a relatively compact structure cannot be obtained. Moreover, the manufacture of the light conductor is relatively complicated due to the different, parallel extending elements.
It is an object of the invention to provide an image display device in which the drawbacks mentioned above are obviated.
In the image display device according to the invention, this object is achieved in that the light conductor comprises a serrated foil which is reflective to a light beam emitted by the light source and having a first direction of polarization, and transparent to a light beam modulated by the light modulation panel and having a second direction of polarization.
The foil is, for example, a reflective polarizer which is made, inter alia, by 3 M and marketed under the name of xe2x80x9cDual Brightness Enhancement Film (DBEF)xe2x80x9d. A similar reflective polarizer is described in U.S. Pat. No. 5,965,247. The reflective polarizer foil may be folded to the desired serrated form by means of two mold parts which are movable with respect to each other. The mold parts may be subsequently removed or connected to the foil for forming an optical element in which the serrated foil is situated.
An embodiment of the image display device according to the invention is characterized in that the serrated foil has a plurality of juxtaposed sawtooth-shaped projections each comprising a first and a second face, a first face situated closer to the light source and facing the light source enclosing a larger angle with respect to the light modulation panel than a further first face situated further remote from the light source and facing the light source.
The angles enclosed by the first faces with respect to the light modulation panel can be chosen to be such that the light beams from the light source are incident on the foil at a desired angle of incidence, are subsequently directed onto the light modulation panel at a desired angle and then leave the serrated foil from the light modulation panel at a desired angle. Since the angle near the light source is larger than on a side remote from the light source, light beams reflected by the light modulation panel will diverge. As described above, a magnifying optical system, onto which the divergent light beams are directed, may be situated on a side of the serrated foil remote from the light modulation panel.